The present invention relates to a transmission system, in particular to a transmission system including a crown wheel and a pinion, especially a transmission system including a crown wheel and a pinion in an axle housing.
A driven axle for automotive vehicles are known whereby a drive shaft aligned generally longitudinally relative to the vehicle drives a pinion which is in meshing engagement with a crown wheel in an axle housing. The crown wheel drives a right hand drive shaft connected to a right hand wheel and also drives a left hand drive shaft connected to a left hand wheel, thereby propelling the vehicle. Typically, the crown wheel will drive the right and left hand drive shafts via a differential assembly.
Oil is provided in the axle housing for lubricating and cooling the crown wheel, a pinion, differential gears and associated bearings. However, the rotation of the crown wheel, the pinion and a differential housing in the oil leads to power losses, thereby increasing the overall fuel consumption of the vehicle.
U.S. Pat. No. 6,299,561 shows a crown wheel which, as it rotates, splashes oil over a wall of the associated housing. A hole in a lower portion of the wall allows oil to drain back to an area where it can again lubricate the crown wheel. In an alternative embodiment, the hole may be replaced by a selectively operable valve. Both embodiments rely on the region surrounding the crown wheel to be emptied by the action of the crown wheel turning. Such a system is not always reliable under certain operating conditions, especially when the crown wheel is turning slowly. It also relies on the various internal surfaces of the housing being arranged to ensure that oil lifted by the crown wheel goes over the wall into the adjacent compartment, rather than simply falling back down into the compartment within which the crown wheel sits.
EP1918613 shows a prefabricated shield fitted around at least a potion of the crown wheel. Oil is splashed out of the region around the crown wheel into another part of the axle housing, and the shield prevents the oil returning to a region where it can lubricate the crown wheel. A valve can be selectively opened to allow oil back into the region around the crown wheel under certain circumstances. Thus, EP1918613 also relies on the crown wheel splashing oil out, in a manner similar to U.S. Pat. No. 6,299,561, and therefore under certain driving conditions will not reliably causes the oil level in the region of the crown wheel to fall.
There is therefore a requirement for an improved transmission assembly.